The present invention relates to electrical plugs in the 30, 60 and 100 amp range; more particularly, the invention relates to an insulating liner which is housed in a plug body and prevents electrical contact between electrical conductors and the plug body.
Heavy duty electrical plugs are used to connect high current, portable electrical equipment to electrical receptacles. The plugs provide for termination of an electrical cord into a number of prongs which are mated to the receptacle. The plug assemblies usually consist of a body, a cover secured to one end of the body where the electrical cord enters and a plug sleeve attached to the opposite end of the body where the prongs are located.
The plugs are designed with adjustable cord gripping and sealing means to allow connection of the plugs to cords of varying diameters. Such a plug design is disclosed in U.S. patent application Ser. No. 725,170 filed Jul. 3, 1991 and the contents of that application are incorporated herein by reference. The plugs are also intended for installation and removal by field personnel without the need for special tools.
Preparation of an electrical cord for attachment to the plug body requires the individual conductors to be exposed and then inserted into the prong assembly where they are held by contact screws. Because each conductor is made up of many strands, some strands can remain exposed creating a risk of short circuit if they come into contact with the outer shell or body of the plug assembly. In addition, heavy duty plugs of the type discussed here are used under harsh conditions and are subject to pulling forces which can cause one of all of the conductors to be pulled out of the prong assembly, also creating the risk of short circuit and injury to personnel.
One way to insulate the area between the conductors and the plug body is to cover the interior of the plug body with an insulating material. However, to properly ground the plug assembly, all metal parts must be in contact in at least one place. Any interference of the insulating material with the proper grounding of the parts could, itself cause a hazard to personnel. In addition, most multi-piece plug assemblies are threaded together requiring the threaded surfaces to be exposed.
There is a need therefore, for an insulator which can be installed between the prong assembly and plug body to prevent electrical contact between conductors and metallic parts of the plug body.
There is a further need therefore, for a plug body insulator which is retained in the plug body making assembly of the plug easy and preventing the loss of the insulator.
There is yet a further need therefore, for an insulator which will rotate inside the plug body as the parts of the plug are assembled and not interfere with electrical grounding connections between different parts of the plug assembly. cl SUMMARY OF THE INVENTION
The insulating liner of the present invention prevents electrical contact between the conductors of an electrical cord and other metallic parts of a heavy duty electrical plug. The liner is cylindrically shaped and fits between the plug body and the prong assembly where the conductors are terminated. To prevent loss or misuse, the liner is retained in the plug body by means of a groove on the inside wall of the plug body. Additionally, the liner rotates within the plug body as the plug is assembled insuring that the grounding post remains electrically connected to the plug body when the plug is assembled.